What did Mendel discover about heredity when he was playing around with plants?

Gregor Mendel artificially cross-pollinated pea plants with a variety of different traits (height, seed color, seed texture and others). When Mendel crossed homozygous tall plants with homozygous short plants, all the peas from these plants produced tall pea plants in the next generation. When Mendel crossed yellow-seeded plants with green-seeded plants, all the peas from these plants produced yellow-seeded pea plants in the next generation. This led Mendel to conclude that when two different characteristics of a trait are crossed, the dominant one tends to be seen in the next generation, and the recessive one tends not to show up. This concept is called Mendel's Law of Dominance and is used to define dominance in modern terms.